Under operator control, a railroad locomotive supplies motive power (traction) to move a train and applies brakes on the locomotive and/or on train railcars to slow or stop the train. The motive power is supplied by electric traction motors responsive to an AC or DC voltage generated by the locomotive engine.
The railroad train comprises three separate brake systems. An air brake system comprises a fluid-carrying brake pipe that extends a length of the train and connects to each rail car. An operator in the lead locomotive controls the fluid pressure in the brake pipe and each rail car responds to the sensed pressure. At each rail car, car brakes are applied responsive to a decrease in the sensed fluid pressure and released responsive to a pressure increase. Each locomotive also comprises an independent pneumatic brake system, coupled to the air brake system, controlled by the operator to apply or release the locomotive brakes.
Each locomotive is also equipped with a dynamic brake system. Activation of the dynamic brakes reconfigures the traction motors of the locomotive to operate as generators, with the locomotive wheels supplying rotational energy to turn the generator rotor winding. Magnetic forces developed by generator action within the traction motors resist wheel rotation and thus create wheel-braking forces. The energy produced by the generator action is dissipated as heat in a resistor grid in the locomotive and removed from the grid by cooling blowers. Use of the dynamic brakes is indicated to slow the train when application of the locomotive independent brakes and/or the railcar air brakes may cause the locomotive or railcar wheels to overheat or when their prolonged use may cause excessive wheel wear. The dynamic brakes may be applied, for example, when the train is traversing a prolonged downgrade. Recently, the Federal Railway Administration mandated a dynamic brake monitor that provides an operator in a lead locomotive of a distributed power train (described below) with the status of the dynamic brakes at each remote locomotive.
A distributed power railroad train comprises a lead locomotive at a head end of the train and one or more remote locomotives in the train consist. A remote locomotive applies power or braking actions (referred to as distributed power/braking) responsive to commands issued by the lead locomotive operator over a distributed power control and communications system. The distributed power (DP) communications system further comprises a communications channel (e.g., a radio frequency (RF) communications channel or a wire-based communications channel) linking the lead and the remote locomotives.
A DP controller generates traction and brake commands responsive to operator-initiated (where the operator is located in the lead locomotive) control of a lead locomotive traction controller (or throttle handle) or a lead locomotive brake controller. The traction or brake commands are transmitted to the remote locomotives over the communications channel. The receiving remote locomotives respond to traction or brake commands to apply tractive effort or to apply or release the brakes. The receiving remote locomotives advise the lead locomotive that the command was received and executed. For example, when the lead locomotive operator operates the lead locomotive throttle controller to apply tractive effort at the lead locomotive (the tractive effort based on a selected throttle notch number) the DP system commands each remote locomotive to apply the same tractive effort (the same notch number) and each remote locomotive replies acknowledging execution of the command. The lead locomotive also monitors remote locomotive status through remote-issued status messages. The lead and remote locomotives can also issue alarm messages.
In general, traction and braking messages sent over the distributed power communications system result in the application of more uniform tractive and braking forces to the railcars, as each locomotive can effect a brake application or brake release at the speed of the communications channel. Distributed power train operation may therefore be preferable for long train consists to improve train handling, especially throttle and dynamic braking applications, and performance. Trains operating over mountainous terrain can realize benefits from DP operation.
The DP control and communications system can be configured in various operational modes that control interactions between the lead and the remote locomotives and execution of lead locomotive commands at the remote locomotives. Two such modes are referred to as synchronous control mode and independent (e.g., front locomotive group/back locomotive group) control mode. In synchronous control all remote locomotives follow the throttle and dynamic brake setting of the lead locomotive. For example, if the lead locomotive operator moves the lead locomotive throttle handle from a notch five position to a notch seven position, the DP system commands each remote locomotive to change to a notch seven throttle position. If the operator moves the throttle handle to a dynamic brake position the DP communications system commands each remote locomotive to the same dynamic brake application.
Typically, the operator configures the locomotives to front group/back group operation to provide better train control when significant terrain gradients are encountered. According to this operational mode, all locomotives assigned to the front group are controlled as the lead locomotive is controlled. The locomotives of the back group also are all identically controlled according to a back group command entered by the lead operator and transmitted to each back group locomotive, which command may differ from the front group command.
In front group/back group or independent control mode the lead locomotive operator assigns each remote locomotive to either a front group or aback group of locomotives, separated by a “fence.” The assignments are dynamically controllable by the operator so that locomotives can be reassigned from the front group to the back group, and vice versa, while the train is operating. Such reassignments can optimize train control. The lead locomotive operator commands each locomotive to front group operation or back group operation by issuing a command over the DP communications system or over an interconnecting conductor.
The remote locomotives assigned to the front group follow the throttle and dynamic brake handle positions of the lead locomotive according to messages sent over the DP communications system. The back group remote locomotives are controlled independently of the front group, but all back group locomotives are identically controlled. The operator operates the DP controller in the lead locomotive to create and transmit a control signal to the back group locomotives. The control signal places each of the back group locomotives in traction or braking operation and further specifies the magnitude (or percentage) of the traction or braking to be applied.
Long distributed power trains are often difficult to control when cresting hills (transitioning from steep uphill to steep downhill grades). As the lead locomotive crests the hill, the train tends to accelerate as an increasing number of cars are on the downhill grade versus the uphill grade. If the train accelerates significantly when stretched over the crest, the operator can lose control of the train, creating a destructively hazardous situation.
When the train is in synchronous mode, if the operator applies the railcar and/or the independent locomotive brakes while one or more remote locomotives and a significant number of railcars are on the uphill side of the crest, these locomotives and railcars may create excessive braking forces for locomotives and railcars farther toward the rear of the train. Also, the locomotives and cars on the downhill grade continue to provide large pull forces, as the applied braking forces have substantially less effect on the downhill grade. This situation can result in the train breaking apart, an obvious and destructive hazard.
To avoid these potentially dangerous situations, the front group/back group independent operational mode can be used, for example, when the train is traversing a mountain. As the train climbs the mountain, the lead locomotive and all remote locomotives provide maximum motive power. When the lead locomotive tops the crest it alone is assigned to the front group, the remaining locomotives are assigned to the back group. The operator controls the from group lead locomotive to apply dynamic brakes or throttle down, while the back group locomotives continue to apply tractive effort to pull the train over the mountain. As a first remote locomotive tops the crest, it is reassigned from the back group to the front group. The first remote automatically follows the dynamic brake application or throttles down to match operation of the lead locomotive. The remaining remote locomotives (e.g., in the back group) continue to apply tractive effort according to the throttle setting of the back group. The process of operator reassignment of the remote locomotives from the back group to the front group continues until the last remote locomotive tops the crest and is reassigned to the front group for application of its dynamic brakes.
Although the DP system includes interlocks to prevent the application of forces that may pull the train apart as locomotives are reassigned from the back to the front group, effective operator control of this scenario can be difficult. Effective operator control depends on the skill level of the operator and many trains break apart due to improper operator control. Operator control may be further complicated by unfamiliar train make-up, travel over unknown terrain, etc.